In engine exhaust systems for trucks, it is a common practice to use a metal flex hose connected with a rigid pipe. It has become important to join the flex hose and the pipe with a coupling which will minimize the leakage of exhaust gases at the joint. The cylindrical wall of the flex hose is inherently somewhat leaky throughout its length and it is desired to provide a coupling with a rigid pipe with a joint which seals against leakage at least as well as the wall of the flex hose itself.
In the prior art, flex hose has been joined to rigid pipe in a lap joint with a band clamp tightened around the overlap region between the flex hose and pipe. However, such an arrangement does not provide a good seal at the lap joint because the clamp is incapable of collapsing the flex hose into sealing engagement with the pipe. In order to make the lap joint, the flex hose must have an inside diameter somewhat greater than the outside diameter of the pipe to permit insertion of the pipe; because of manufacturing tolerances, the difference in diameters is sometimes greater than that needed for insertion and, in such instances, the joint exhibits high leakage.
Also in the prior art, lap joints between flex hose and rigid pipe are known which utilize a wide band clamp which spans the rigid pipe and the flex hose and is tightened so that it is in close engagement with the outer surface of both the flex hose and the pipe to thereby seal the joint. The close engagement may be achieved by pre-forming the band clamp to accommodate the smaller diameter of the rigid pipe. Alternatively, the band clamp is of uniform diameter prior to installation and is deformed sufficiently during tightening to provide engagement thereof with both the flex hose and pipe. Lap joints of this type are disclosed in U.S. Pat. Reissue 30,042 granted Jul. 10, 1979 to Heimstra, et al.; U.S. Pat. No. 4,261,600, granted Apr. 14, 1981 to Cassel; and U.S. Pat. No. 4,312,526 granted Jan. 26, 1982 to Cassel. While certain lap joints of this type are meritorious in some respects, they are disadvantageous in respect to cost and materials. Further, this type of clamp does not lend itself to applications in which the lap joint is located immediately adjacent an elbow in the rigid pipe because there is not enough straight pipe to accept the band clamp portion.
Lap joints for coupling two rigid pipes are known in the prior art in which the outer pipe end is adapted to be collapsed by use of a band clamp. In U.S. Pat. No. 4,270,689 granted Jun. 2, 1981 to Canfield, lap joint is disclosed in which the outer pipe is provided with take-up slots in the overlap region of the pipe-ends to facilitate the collapsing of the outer pipe-end into engagement with the inner pipe by a band clamp. In this arrangement, the take-up slots do not extend through the end of the pipe; instead, they terminate at a point inwardly of the pipe-end and are sometimes referred to as "captured" slots. U.S. Pat. No. 4,113,289 granted Sep. 12, 1978 to Wagner et al. describes a lap joint for rigid pipes which utilizes a set of captured slots in the end of the outer pipe and a set of relief slots which are disposed adjacent respective captured slots. The relief slots extend all the way to and are open at the end of the outer pipe. U.S. Pat. No. 4,629,226 granted Dec. 16, 1986 to Cassel et al. describes a rigid pipe lap joint having an outboard slot which extends inwardly from the pipe-end and an inboard slot circumferentially offset and extending inwardly from the inner end of the outboard slot. The end walls of the adjacent ends of the inboard and outboard slots are disposed in edge-to-edge engagement with each other when the overlap region of the outer pipe is clamped into close fitting engagement with the inner pipe.
A general object of this invention is to provide an improved lap joint for coupling a rigid pipe to a flex hose and to overcome certain disadvantages of the prior art.